Preform cutting elements for rotary drill bits

Abstract

A preform cutting element for a rotary drag-type drill bit comprises a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface. The front surface of the facing table is formed with a chip-breaking formation which is located adjacent the cutting edge and is shaped to deflect transversely of the front surface of the facing table cuttings which, in use, are removed by the cutting edge from the formation being drilled. The chip-breaking formation may comprise a peripheral groove or rebate, or an upstanding ridge or insert.

What is claimed: 
     
       1. A preform cutting element for a rotary drag-type drill bit, comprising a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface, the front surface of the facing table being formed with a groove which is smoothly and continuously curved in cross section and is located adjacent at least a part of the cutting edge and is shaped to deflect transversely of the front surface the facing table cuttings which, in use, are removed by the cutting edge from the formation being drilled. 
     
     
       2. A cutting element according to claim 1, wherein the groove has an outer edge which is spaced inwardly from the cutting edge by a substantially constant distance. 
     
     
       3. A cutting element according to claim 1, wherein the groove is part circular in cross-section. 
     
     
       4. A preform cutting element for a rotary drag-type drill bit, comprising a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface, the front surface of the facing table being formed with a groove which is located adjacent at least a part of the cutting edge, and there being formed in the groove a plurality of protrusions spaced apart longitudinally of the groove. 
     
     
       5. A cutting element according to claim 4, wherein each protrusion has an upper surface which lies at substantially the same level as the front surface of the facing table. 
     
     
       6. A cutting element according to claim 4, wherein each protrusion extends transversely across the groove. 
     
     
       7. A cutting element according to claim 6, wherein each protrusion extends across substantially the full width of the groove. 
     
     
       8. A cutting element according to claim 4, wherein each protrusion is elongate and inclined at an angle of 90° to the length of the groove. 
     
     
       9. A cutting element according to claim 4, wherein each protrusion is elongate and inclined at an angle of less than 90° to the length of the groove. 
     
     
       10. A cutting element according to claim 9, wherein all the protrusions are inclined at substantially the same angle to the length of the groove. 
     
     
       11. A cutting element according to claim 9, wherein adjacent protrusions are inclined at opposite and equal angles to the length of the groove. 
     
     
       12. A preform cutting element for a rotary drag-type drill bit, comprising a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface, the front surface of the facing table being formed with a groove which is located adjacent at least a part of the cutting edge, a portion of the front surface of the facing table between the groove and the cutting edge being configured to upstand from that surface. 
     
     
       13. A cutting element according to claim 12, wherein said portion of the surface is formed with upstanding serrations which fill the space between the outer edge of the groove and the cutting edge, the cutting edge then being defined by parts of said serrations. 
     
     
       14. A preform cutting element for a rotary drag-type drill bit, comprising a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface, the front surface of the facing table being formed with a peripheral rebate at the junction between the front surface and the peripheral surface of the front facing table, the cutting edge being defined by the junction between the rebate and the peripheral surface. 
     
     
       15. A cutting element according to claim 14, wherein the rebate is smoothly and continuously curved in cross-section. 
     
     
       16. A cutting element according to claim 14, wherein the rebate is angular in cross-section. 
     
     
       17. A cutting element according to claim 14, wherein there is formed in the rebate a plurality of protrusions spaced apart longitudinally of the rebate. 
     
     
       18. A cutting element according to claim 17, wherein each protrusion has an upper surface which lies at substantially the same level as the front surface of the facing table. 
     
     
       19. A cutting element according to claim 18, wherein each protrusion extends transversely across the rebate. 
     
     
       20. A cutting element according to claim 19, wherein each protrusion extends across substantially the full width of the rebate. 
     
     
       21. A cutting element according to claim 19, wherein each protrusion is elongate and inclined at an angle of 90° to the length of the rebate. 
     
     
       22. A cutting element according to claim 19, wherein each protrusion is elongate and inclined at an angle of less than 90° to the length of the rebate. 
     
     
       23. A cutting element according to claim 22, wherein all the protrusions are inclined at substantially the same angle to the length of the rebate. 
     
     
       24. A cutting element according to claim 22, wherein adjacent protrusions are inclined at opposite and equal angles to the length of the rebate. 
     
     
       25. A preform cutting element for a rotary drag-type drill bit, comprising a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface, the front surface of the facing table being formed with a peripheral rebate at the junction between the front surface and the peripheral surface of the front facing table, the cutting edge being defined by the junction between the rebate and the peripheral surface, the rebate including a bottom wall extending away from the cutting edge and a side wall upstanding from the bottom wall and extending towards the front surface of the facing table, said side wall including at least two portions on each side of an apex directed towards the cutting edge whereby, in use, chips removed by the cutting edge and passing across the rebate are deflected to both sides of the apex. 
     
     
       26. A preform cutting element for a rotary drag-type drill bit, comprising a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface, the front surface of the facing table being formed with at least one protrusion which upstands from said front surface of the facing table. 
     
     
       27. A cutting element according to claim 26, wherein the protrusion comprises an elongate ridge formed on said front surface adjacent the cutting edge. 
     
     
       28. A cutting element according to claim 27, wherein the ridge has an outer edge which is spaced inwardly from the cutting edge. 
     
     
       29. A preform cutting element for a rotary drag-type drill bit, comprising a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface, the front surface of the facing table being formed with a recess which is smoothly and continuously curved in cross-section and which extends across a major part of the front surface and has an outer peripheral edge which is spaced inwardly from the cutting edge. 
     
     
       30. A cutting element according to claim 29, wherein the recess is concentric with the front surface of the facing table and the outer edge of the recess is spaced a constant distance from the cutting edge. 
     
     
       31. A preform cutting element for a rotary drag-type drill bit, comprising a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface, the element including an insert which is received in a socket in the cutting element adjacent the cutting edge thereof, the insert including a part which is upstanding from the front surface of the facing table. 
     
     
       32. A cutting element according to claim 31, wherein the insert and socket are substantially circular in cross-section. 
     
     
       33. A cutting element according to claim 31, wherein at least the part of the insert which is received in the socket is cylindrical. 
     
     
       34. A cutting element according to claim 31, wherein the socket and insert extend through substantially the whole thickness of the cutting element. 
     
     
       35. A cutting element according to claim 31, wherein the upstanding part of the insert is domed. 
     
     
       36. A cutting element according to claim 35, wherein the outer periphery of the domed part of the insert lies at the same level as the front surface of the facing table. 
     
     
       37. A cutting element according to claim 31, wherein the upstanding part of the insert has a front surface which is inclined away from the front surface of the facing table as it extends away from the cutting edge. 
     
     
       38. A cutting element according to claim 37, wherein the edge of said inclined surface nearest the cutting edge of the facing table lies at the same level as the front surface of the facing table. 
     
     
       39. A cutting element according to claim 31, wherein the insert comprises a front layer of superhard material bonded to a substrate of less hard material, the superhard material forming a front surface on the upstanding part of the insert.